In response to a growing need to improve the efficiency of radio communications systems, a Digital Mobile Radio (DMR) communications standard establishes protocols and other system requirements for communications on private mobile radios. Any DMR standards or specifications referred to herein may be obtained by contacting ETSI at ETSI Secretariat, 650, Route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE. Private mobile radios include radios, other than mobile telephones, such as mobile radios, portable radios, and the like. The DMR standard supports simultaneous and independent calls on a single channel. In particular, according to the standard, a 12.5 Kilohertz (kHz) channel is divided into two alternating timeslots. Each timeslot acts as a separate communications path for two or more radios, where each radio operating on the channel communicates on an assigned timeslot.
Radios operating on the channel synchronize traffic on the channel by using a timing reference. To minimize channel traffic associated with radios requesting the timing reference when there is no timing reference signal for radios operating on the timeslots on the channel, one radio operating on the channel is selected as a channel timing leader. The channel timing leader intermittently transmits a timing signal in at least one channel timing (CT) message to other radios operating on the channel. The other radios operating on the channel adjust their transmission clocks based on the timing signal transmitted from the timing leader.
The timing leader typically transmits the CT message at predefined intervals over a long period. However, constant beaconing of the CT message by the timing leader can impact the longevity of the timing leader's power source if, for example, the power source is a battery. The timing leader is also subject to move out of range or otherwise fail. There is currently no efficient manner to transition the functions of the timing leader from one radio to another radio operating on the channel.
Accordingly, there is a need for a method and apparatus for automatically switching the functions of the timing leader radio to another radio operating on the channel.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.